Unidentified test unit Death Star

At some point prior to the Galactic Civil War, a test unit model of the Death Star was developed by the Galactic Empire as a means to test the concept of the battlestation.

During the Galactic Civil War, the Rebel Alliance attacked the test unit, believing it to be the actual Death Star. After storming through the Stormtroopers assigned to guard it, they eventually reached the control room, only to discover the truth of the station. After the Rebel victory, the Imperial troops evacuated. Darth Vader later ordered for the station to self-destruct.

Text and facts from the “Unidentified test unit Death Star” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.